Abstract
The periodic removal of the sediments deposited inside artificial reservoirs can be carried out through the flushing methodology, in which the bottom outlets of the dam are opened to let the water flow through the gates, eroding and transporting downstream the sediments. However, these cleaning maneuvers generate marked variation both in the flow rate and in the Suspended Sediment Concentration (SSC) in the river reaches downstream of the dam and may produce negative effects on the riverine ecosystems and biotic communities, especially on fish. In particular, the alteration of river hydraulic parameters (i.e. water depth and flow velocity), that can let to the worsening of the fishes suitable habitat, and the excessive turbidity (i.e., high SSC values) combined with high SSC values may provoke a possible worsening of habitat suitability for fish that could give rise to increased animal stress. The scientific literature provides individual tools to model the effects of the varied river hydraulic characteristics and the increased fine sediment load, separately. Moreover, due to the simultaneous occurrence of flow rate variation and SCC increase, it is advisable to combine the two approaches to obtain a comprehensive and representative fish habitat modelling during flushing events. Therefore, the present work aims to propose an innovative methodology for the fish habitat modelling during the sediments’ removal operations, in order to minimize their ecological effects while optimizing sediment management in the reservoirs. With the aim of generalizing our results, different river morphologies, life stages of the chosen freshwater fish species – the European grayling (Thymallus thymallus, L. 1758) – and three possible volumes of removed sediment were considered. Results showed that grayling habitat suitability tended to decrease with increasing flow rates and SSC no matter the life stage. However, interestingly, they showed also that it was preferable to increase the water discharge to reduce the flushing event duration when considered high volumes of released sediments.